Evaluation of two enzyme immunoassays for detection of immunoglobulin G antibodies to mumps virus

To determine suitability for national serosurveys, we compared two commercial enzyme-linked immunosorbent assays (ELISAs) for mumps antibody, Enzygnost Anti-Parotitis-Virus/IgG (which uses a whole-virus antigen) and Microimmune Mumps IgG Screen ELISA (which uses a recombinant nucleoprotein antigen), by testing 1,915 opportunistically collected sera submitted to diagnostic laboratories across Australia in 1997 to 1998. The proportion of positive results increased with age in both ELISAs but was significantly higher with the Microimmune than with the Enzygnost ELISA overall (88% versus 63%; P < 0.01) and in all age groups. However, the proportion of equivocal results was significantly higher with the Enzygnost than with the Microimmune ELISA (9% versus 4%; P < 0.01). Of the 572 sera with discrepant or equivocal results, 508 had sufficient sample remaining to perform the neutralization test (NT). A proportion with concordant results in both ELISAs were also tested by the NT. For sera with discrepant results, there was significantly better agreement between the NT and Microimmune than between the NT and Enzygnost (310/444 [70%] versus 1351348 [39%]; P < 0.01). Of 64 sera with equivocal Microimmune results, 45 (70%) were positive in the NT compared with 140 of 160 (88%) equivocal Enzygnost results (P < 0.01). Compared with the NT, the Microimmune ELISA is more sensitive (96% versus 80%) but apparently less specific (36% versus 85%) than the Enzygnost ELISA. However, this is likely to be due to the generally lower sensitivity of the NT, since the Microimmune results reflect expected seroprevalence, based on vaccine uptake in the age groups studied. We conclude that the Microimmune ELISA is a more appropriate assay than the Enzygnost ELISA for estimation of mumps seroprevalence.